This invention relates to a system for applying a plastic liner to oil field country tubulars, such as well tubing, and a joint formed by such tubing incorporating the plastic liner. More particularly, flanges attached to the liner have both radial and circumferential sealing surfaces to positively prevent fluid in the well tubing from contacting either the interior of the tube or a connecting collar.
Well tubing has have been utilized for many years to provide a flow path for fluids passing to and from the well reservoir. The well tubes are inserted into a well that has been drilled and are used to inject fluids into the well reservoir to raise pressure and fluid levels, and to remove oil or gas from the completed well. The fluids cause abrasion and deterioration of the tubes and the collars connecting them. Therefore, it is well known to provide tubes with a liner in order to minimize the abrasion and the deterioration of the tube. The liner may take the form of a layer of cement or a plastic coating applied to the interior surface of the tube. The interior of the tube may also be coated or covered with other materials which are relatively inert to the fluids passing through the well tube.
A series of tubes are typically attached together end to end by collars which threadingly engage adjacent ends of the tubes. The ends of the tubes and the collar have corresponding threads, usually tapered, such that rotation of the collar and tubes relative to each other draws the ends of the well tubes toward each other in secured relationship. In order to prevent deteriation of the collar and leakage at the joint area, it has been proposed to provide end seals on the ends of the tubes by either a separate flange piece attached to the tube liner or by rolling over the tube liner to cover the end of the tube. However, these systems have not completely alleviated the problems, since the junction between adjacent flanges or between the rolled over liners often does not provide an adequate seal. Furthermore, rolling or otherwise forming the liner over the end of the tube requires threads to be formed thereon to match those of the collar. As a practical matter, this is difficult, if not impossible, to accomplish and still maintain reasonable production costs. The wear of the threaded lining occasioned by the installation and removal of the collars eventually causes the lining seal to deteriorate thereby necessitating a complete re-fitting of the liner.
It is also known to provide rigid liners for underground pipelines by forming the liner from a plastic material with an initial outer diameter greater than the interior diameter of the pipeline. The liner diameter is reduced prior to inserting it into the pipeline. After insertion, the liner is expanded into contact with the pipeline by drawing a heating element through its interior, by physical expansion using an interior plug, by application of internal pressure or simply letting the liner expand towards its initial diameter by relaxation.
It is also known to form a rigid plastic liner with an outer diameter less than the inner diameter of a section of pipe. Subsequent to insertion of the liner, flanges are attached to each end of the liner and a heated fluid is passed through the liner to cause it to expand and contact the interior of the pipe section. The axially facing end of the flange is brought into sealing engagement with a corresponding sealing surface of an adjacent flange when the pipeline sections are bolted together.